Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to electronic article surveillance and electronic article identification devices, and more particularly to an electronic article surveillance tag that includes electronic article identification, and an associated system and method.
2. Description of the Related Art
It is well known to provide electronic article surveillance (EAS) systems to prevent or deter unauthorized removal of articles from a controlled area. In a typical system, tags designed to interact with an electromagnetic field located at the exits of the controlled area are attached to articles to be protected. If a tag is brought into the field or xe2x80x9cinterrogation zonexe2x80x9d, the presence of the tag is detected and appropriate action is taken, such as generating an alarm.
There are several types of EAS systems presently available that detect EAS tag signals by harmonic or field disturbance detection. U.S. Pat. No. 3,810,147 discloses an EAS marker or tag that includes an LC resonant circuit. The tag is typically interrogated by transmitting a swept frequency including the resonant frequency of the tag. The tag is detected by a receiver in the interrogation zone that detects a change in the interrogation field at the tuned frequency due to the resonance of the LC circuit. Manufacturing a tag with a precise resonant frequency requires stringent manufacturing tolerances, which can result in a more expensive tag. To manufacture a more affordable tag, manufacturing tolerances are relaxed resulting in a resonant frequency that may shift slightly from tag to tag. To interrogate the more affordable tags with variances in resonant frequency, a swept frequency is transmitted, which can require higher power usage than transmitting a discrete frequency.
An improved tag and associated EAS system utilizes an LC resonant circuit that includes a magnetic material that exhibits a xe2x80x9cgiant magneto-impedancexe2x80x9d (GMI) effect when exposed to a magnetic field. As fully described hereinbelow, a GMI effect is a substantial change in impedance of the magnetic material when exposed to a magnetic field. The magnetic material can be a wire or ribbon and is connected to the LC circuit by soldering, plating, or etching to form part of the circuit. Additional information on magneto-impedance material can be found in a various published sources, such as U.S. Pat. No. 5,994,899.
A transmitted low frequency magnetic field interacts with the magnetic material to produce the GMI effect. The GMI effect due to the magnetic field causes the impedance of the magnetic material to change. The change in impedance of the material changes the resistance of the material causing the quality factor (Q) of the LC circuit to change. The change in Q results in a change in the output level of the LC circuit at resonance. In effect, the LC circuit and magnetic material modulate the transmitted resonant or carrier frequency with the low frequency magnetic field. The tag thus produces sidebands of the resonant frequency, which can be detected by suitable detection equipment.
The tag is interrogated by simultaneously transmitting a first signal at the LC circuit""s tuned resonance frequency and a second signal comprising a low frequency alternating magnetic field. Because of the magnetic material, the tag mixes the resonant xe2x80x9ccarrierxe2x80x9d frequency and the low frequency magnetic field, forming sidebands of the resonant frequency that can be detected by a suitable EAS receiver.
Sideband detection is an improvement over harmonic or field disturbance detection. In the detection of harmonics or a change in the fundamental, the carrier signal itself is a source of noise. The signals that are being detected are small, so even a small amount of carrier noise masks the desired signal. With sideband detection, the carrier frequency is not a noise source that masks detection of the sidebands. In addition to the sideband generating tag described above, U.S. Pat. No. 4,736,207, discloses a microwave tag which includes a tuned dipole antenna and a nonlinear circuit device that mixes two interrogate signals and re-radiates the first signal modulated by the second signal.
In addition to EAS, there is presently a desire to expedite and facilitate the removal of articles from controlled areas by gathering identification data about the article. As used herein, identification data means any data to be gathered, stored, or used pertaining to an article or object to be protected, monitored, retained, sold, inventoried, or otherwise controlled or distributed in some manner. For example, retail establishments desire to gather information pertaining to article identification, price, and pertinent inventory control data. Presently, bar codes provide some of this type of data. However, bar codes can only provide a small amount of read only data, and the bar code reader or scanner must be visually aligned with the bar code to properly read the bar code attached to the article, slowing the checkout or inventory process.
Radio frequency identification (RFID) utilizes radio frequency (RF) interrogation and reply frequencies to perform electronic article identification (EAI) functions. In RFID, a tag that responds with RF identification information, in response to an RF interrogation signal, is attached to an article to be identified. At present, RFID tags are well suited to provide article identification information, pricing information, inventory control, and can receive and store information such as the date and place of sale, sales price, and article manufacturing authenticity information. However, RFID tags are not well suited to EAS applications because of limited detection range as well as being prone to shielding and detuning when proximate certain materials, which can result in missed EAS detection. Presently EAS tags and RFID tags must both be attached to an article if identification and protection of the article are desired.
U.S. Pat. No. 5,859,587 discloses an RFID and EAS tag integrated within the same tag housing. The RFID and EAS functions in the ""587 disclosure are electrically separate, discrete functions that are located within one enclosure. There is presently a desire for a tag that combines both EAS and EAI functions.
In accordance with the present invention, there is provided an electronic article surveillance and identification tag and system. In a first aspect of the present invention, the tag couples energy from a radiated energy source, which includes first and second radiated signals. A mixing member in the tag mixes the first and second signals to produce a sideband of the first signal, which is re-radiated by the tag. A controller switches the mixing member into and out of the circuit according to a code stored within the controller that is associated with an article to be identified. As the mixing member is switched in and out, the sideband produced by the tag will be radiated in a sequential manner according to the stored code. A receiver detects the sideband, and a decoder recovers the stored code according to the sequence of received sideband emissions from the tag.
Radiated energy received by the tag provides power for the controller. As long as the controller is powered, the tag will continue to re-radiate the generated sideband in a sequence corresponding to the stored data code. When the coupled energy drops below a pre-selected minimum level, the controller becomes deactivated. When the controller is deactivated, the mixing member remains in the circuit and continues to mix the first and second signals to produce the sideband. The sideband is continually generated and re-radiated until the tag is removed from the radiated energy field. The tag thus performs as an EAS tag and an EAI tag when the coupled energy is above a pre-selected minimum level, and continues to perform as an EAS tag when the coupled energy drops below the pre-selected minimum level thus deactivating the controller.
In one embodiment of the present invention, an inductor and a capacitor forming an LC circuit having a pre-selected resonance frequency couples the radiated energy, which contains the first and second signals. The mixing member is a segment of magnetic material exhibiting a GMI effect when exposed to a magnetic field. A GMI effect is a substantial change in the material""s impedance when exposed to a magnetic field, as fully described hereinbelow.
In one implementation, the magnetic member is a wire or ribbon connected to the LC circuit that changes resistance when exposed to an alternating magnetic field. The change in resistance of the magnetic member changes the Q of the LC circuit. When the radiated energy received by the LC circuit includes its resonance frequency and a lower frequency magnetic field, the magnetic member changes the Q of the circuit resulting in modulation of the two signals. Modulation or mixing of the two signals generates sidebands of the resonance frequency, which are then detectable in conventional manner. The controller controls switching the mixing member into and out of the circuit.
The controller receives power from the LC circuit through a power rectifier, and includes a switch connected across the magnetic member that shorts the magnetic member whenever the switch closes. Switch control is provided by a logic control unit that is connected to a non-volatile memory that stores a pre-selected code associated with an article to be identified. Sideband generation stops when the switch closes and shorts the magnetic member. The sideband can thus be sequentially generated by sequentially closing and opening the switch. If the switch closure corresponds to the digital data code stored in the non-volatile memory, the sideband will be generated according to the stored code. A detector receives the sideband and a decoder can reconstruct the stored digital code from the detected sideband emissions. When the coupled power to the rectifier drops below a pre-selected minimum level, the power rectifier deactivates the controller. The switch is normally open (NO) and remains in the open state when the controller is deactivated. Thus the magnetic member continues to be in the LC circuit mixing the two signals when the controller is deactivated, and the tag functions as an EAS tag.
The tag can be made of discrete components or made on a substrate having conductive layers formed thereon to provide the inductor, and the capacitor. The magnetic member and/or controller may also be formed on the substrate, or may be separate and connected to the components on the substrate.
In an alternate embodiment of the present invention, a dipole antenna tuned to the is microwave frequency band couples the radiated energy. The mixing member is a diode, or other non-linear circuit device having electrical characteristics similar to a diode. The diode is activated by an electric field, and modulates two signals together in a well-known manner, see e.g., U.S. Pat. No. 4,736,207.
The controller switch is connected across the diode and performs as described hereinabove for the magnetic member. When the switch is open the tag containing the diode and dipole antenna receives and modulates the two radiated signals forming the sidebands, which are re-radiated by the tag. When the switch is closed, the diode is shorted, and the sidebands are not generated. As above, the switch can be sequentially opened and closed according to the stored digital data code. A detector can detect the sideband and a decoder can reconstruct the digital data code associated with the article to be identified.
When the coupled energy falls below a pre-selected minimum level, the controller is deactivated and the switch remains open. The sidebands are continually generated while the tag remains in the radiated energy field of the two signals. Thus, when the controller is deactivated, the tag behaves as a conventional microwave EAS tag providing theft deterrence.
According to a second aspect of the present invention, an EAS and EAI system is provided that transmits a first and second signal at a first and second frequency, respectively, which are mixed by a tag having a signal mixing member which generates and re-radiates sidebands of the first frequency modulated by the second frequency. The tag includes a controller powered by the transmitted signals that switches on and off the mixing member according to a stored data code that is associated with an article to be identified. A detector detects the re-radiated sidebands, and a decoder decodes the data code according to the received sidebands. The data code is stored in non-volatile memory in the tag, and can be changed by transmission of a proper reprogramming code to the tag. The non-volatile memory can be an electronically erasable programmable read-only memory (EEPROM) or equivalent device.
In a first implementation, the tag includes an LC circuit and a mixing member that is made of a magnetic material that exhibits a GMI effect when exposed to a magnetic field. The first signal is radiated at the resonant frequency of the LC circuit and the second signal, which is at a lower frequency than the first frequency, is the magnetic field that provides the GMI effect.
In a second implementation, the tag includes a dipole antenna and a diode signal mixing member, which is activated by an electric field. The resonant frequency of the tag is in the microwave frequency band. The second signal is lower in frequency than the first signal and produces the electric field that activates the diode.
In a third aspect of the present invention, a method of operation of an EAS and EAI system is provided including providing a tag which includes a tuned circuit and a signal mixing member. Transmitting a first signal at a resonant frequency of the tuned circuit. Transmitting a second signal at a frequency that is lower than the first signal, the second signal activating the signal mixing member. Sequentially turning on and off the signal mixing member according to a pre-selected data code associated with an article to be identified. Detecting a sideband of the first signal, the sideband being generated by the signal mixing member mixing the first and the second signals. And, decoding the pre-selected data code from the detected sideband.
Accordingly, it is an object of the present invention to provide an electronic article surveillance tag that also provides electronic article identification such as RFID.
It is a further object of the present invention to provide an EAS and RFID tag that includes a signal mixing member that mixes two signals to produce a detectable sideband signal, and includes a controller that sequentially switches on and off the mixing member according to a stored data code associated with an article to be identified.
It is another object of the present invention to provide an EAS and RFID system to interrogate at two frequencies, detect a sideband signal, and decode from the detected sideband signal a stored data code associated with an article to be identified.
It is yet a further object of the present invention to provide a method of operation of an EAS and RFID system that interrogates at two frequencies, detects a sideband signal, and decodes from said detected sideband signal a stored data code associated with an article to be identified.
Other objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of the preferred embodiment of the invention.